Electronic directing system

ABSTRACT

The present invention relates to an arrangement and electronic navigational control system for a self-propelling device ( 5 ), preferably a lawn-mowing robot. The system comprises at least one navigational control system ( 3 ) connected to at least one signal generator ( 1 ) and a sensing unit arranged at the self-propelling device ( 5 ). The sensing unit senses at least one, in the air medium propagating, time and space varying magnetic field, at least transmitted via the navigational control station ( 3 ) and in turn retransmits at least one signal processed by the unit to at least one driving source which contributes to the device&#39;s movements across the surface. The system comprises means by which the signal generator ( 1 ) sends a current through the navigational control station ( 3 ), the current generating the time and space varying magnetic field, whereby the sensing unit comprises means by which the device ( 5 ) is manoeuvred based on the properties of the sensed magnetic field.

TECHNICAL FIELD

The present invention relates to a procedure and an electronicnavigational control system for a self-propelling device, preferably alawn-mowing robot. The system comprises at least one navigationalcontrol station connected to at least one signal generator and a sensingunit arranged at the self-propelling device. The sensing unit senses atleast one time and space varying magnetic field propagating in the airmedium, at least transmitted via the navigational control station and inturn retransmits at least one signal processed by the sensing unit to atleast one driving source that contributes to the movements of the deviceacross a surface. The invention relates to an electronic navigationalcontrol system comprising means by which the signal generator sends acurrent through a navigational control station. The current generates atime and space variable magnetic field, whereby the sensing unitcomprises means by which the robot is controlled based on the propertiesof the sensed magnetic field.

TECHNICAL BACKGROUND

The thought of developing fully automatic working tools is old. Suchworking tools may relate to devices for cutting grass, which from now onwill be called a robot. Despite this fact, such products have only inrecent years reached the market. One such example is the robotic lawnmower Auto Mower™. It mows a surface by moving across the surface withinthe area to be worked on. Loops are used to keep the robot within adelimited area. These comprise electrical conductors transmittingsignals, which are sensed by a sensing device onboard the robot and thuscontrolling the movements of the robot from outside. The loops are used,for instance, to mark the boundary, which the robot must not exceed andto make the robot distance itself from the loop.

The sensing device normally consists of at least a receiving device forsensing for instance magnetic fields, a control unit connected to thereceiving device to process the received signal and a motor control unitconnected to the control unit to control the movements of the robotbased on the processed information. When the robot approaches a loop,the system senses a change in magnetic field strength. The control unitprocesses the information and chooses to direct the robot in a certaindirection dependent on which function that is activated.

A disadvantage with the previous loop system is that the robot follows alaid down loop in order to direct the robot towards a certain place,which can be represented by a charging station for the robot's batteriesand/or parking place for when the robot is not working. To direct therobot towards this place, one must necessarily put down a navigationalcontrol station comprising a big closed loop so that the robotfrequently intersects it during its normal movements and thereby has thepossibility to start following the loop. A further disadvantage is thatpresent types of navigational control stations normally direct the robotalong a path, which is repeated each time the robot is directed. Therebythe robot's wheels will cause wear along the surface area they pass. Thepresent invention has been developed with the intention to remedy thesedisadvantages.

SUMMARY OF THE INVENTION

In the present invention said sensed magnetic field, in an area mainlywithin the range of the navigational control station, at least at onepoint of time has different directions.

DESCRIPTION OF DRAWINGS

The invention is described more in detail in conjunction with thepreferred embodiments and with reference to the enclosed drawings.

FIG. 1 shows a control system in accordance with the subject invention.

FIG. 2 shows a diagram presenting signals in the control systemaccording to FIG. 1.

FIG. 3 shows a self-propelling device for the navigational controlsystem according to FIG. 1.

FIG. 4 shows an embodiment of the control station according to FIG. 1.

FIG. 5 shows an alternative embodiment of the navigational controlstation according to FIG. 1.

FIG. 6 shows a top view of the vertical magnetic field, as sensed by thesensing unit, around the navigational control station according to FIG.4 and 5.

FIG. 7 shows a side view of the field direction of the vertical magneticfield, as sensed by the sensing unit, for the navigational controlstation according to FIG. 5.

FIG. 8 shows an alternative embodiment of the control station accordingto FIG. 4.

FIG. 9 shows a top view of the vertical magnetic field, as sensed by thesensing unit, around the navigational control station according to FIG.8.

FIG. 10 shows a side view of the field direction of the verticalmagnetic field, as sensed by the sensing unit, for the navigationalcontrol station according to FIG. 8.

FIG. 11 shows two patterns of movement possible for the robot whilesensing the magnetic field generated by the navigational control stationaccording to FIG. 4 and 5.

FIG. 12 shows one pattern of movement possible for the robot whilesensing the magnetic field generated by the navigational control stationaccording to FIG. 8.

DESCRIPTION OF A PREFERRED EMBODIMENT

Examples of embodiments of a control system in accordance with theinvention are shown in the figures. The examples of the embodimentsshall not be interpreted as a limitation of the invention but their onlypurpose is to concretely shed light on preferred embodiments of thecontrol system according to the invention. This is to further clarifythe thought behind the invention.

The intention of the invention relates to developing a system using anavigational control station to direct a robot towards a specifictarget. The station area of the navigational control station,constituting the range of the station, shall be so small that the robotnormally cannot move within this area and if the area is verticallypositioned, the robot will never move inside the area. Besides, themagnetic field generated by the station shall be so strong that it canbe sensed by the robot within a navigational control area extendinginside and outside the station area. The generated magnetic field isused for the navigation of the robot within the navigational controlarea. The navigational control station can comprise a loop, a remotesystem, which, in certain cases, is sufficient to control the robot. Thenavigational control system can alternatively constitute or comprise twodifferent loops, one proximity system, which increases the possibilitiesto influence the direction in which the robot is approaching its target.Another alternative is to use the two loops for creating both theproximity system and the remote system. A loop is defined as a closedloop of a conductor, wound in one or many loops, whereby the parallelsections of the conductor are not positioned so close to each other thatthe interfering magnetic fields do suppress each other completely.

The magnetic field generated by the remote system will propagate withinan area defined by the navigational control range, whereby the robotsenses the field direction and/or amplitude at the position of therobot. The robot can for example use this information to move closer toor further away from the station, to carry out circular movements aroundthe station or to stop or possibly turn in relation to the station. Themagnetic fields generated by the different loops in the proximity systemwill be opposed and superimpose. Consequently, they will propagatewithin an area defined by the navigational control range of theproximity loop, which, due to the co-operation between the two fields,will be significantly smaller than the navigation control range of theremote loop. By letting the proximity system co-operate with the remotesystem, the robot is, apart from the possibilities offered by the remoteloop, enabled to approach the loop in a preferable way, e.g. so that therobot can be brought into such a position that a charging device at thenavigational control station can charge the batteries of the robot.

FIG. 1 shows a navigation control system in accordance with theinvention. A signal generator 1 generates the current that is fedthrough the outer loop 2 and the navigational control station 3. Theouter loop 2 is not necessary but shall be seen as an example of thetype of loops used to encircle an area within which the robot isintended to move. The current fed through this loop generates a magneticfield that propagates out from the loop, by which the robot determineswhether it is inside or outside the area defined by the outer loop. Thearea covered by the navigational control station 3 defines the stationarea. In the figure, the navigational control station 3 is representedby a block or a box.

The navigational control station 3 in the figure is horizontallypositioned, but it might as well be positioned in any other way, e.g.vertically. One possibility is to position certain parts of theterminal, e.g. the remote system, in one direction and other parts, e.g.the proximity system, in a different direction. The intention of thenavigational control station is mainly to generate a magnetic field thatpropagates within a navigational control area inside or outside of theterminal area, whereby the robot, within the navigational control area,can navigate in relation to the terminal

When selecting the type of signal (frequency, amplitude) in the currentfed through the outer loop 2 and the navigational control station 3, itis necessary to consider the properties of the electric conductor to beused. Since the conductor normally has inductive properties, theactivation of a voltage pulse across a conductor will result in a delayof the rise of the corresponding current pulse up to the current levelcorresponding to the voltage across the conductor and the conductor'sresistance, i.e. Ohm's law (I=U/R). Thus, during the initial stages ofevery current pulse, there will be a period of time during which thenavigation control system does not work in accordance with stationaryelectric theory.

The navigation control station 3 comprises the significant part of theinvention. The current fed through this part generates a time and spacevariable magnetic field used by the robot to navigate. The station isusing one or many electric conductors wound as loops. The size/range ofthe navigational control area is influenced by the number ofampere-turns fed through the loops. With a current of 1 A in a loop ofthree turns, an equivalent range is generated as with 3 A in an equallysized one-turn loop. That means that the navigational control stationthat preferably uses a loop with several turns, differs from the outerloops that have been used and are used to define areas and enable therobot to follow a loop. These types of outer loops are using lowercurrent and more important and are only drawn one turn around a biggeror smaller area. They are not intended to create a large navigationalcontrol area within which the robot can sense the magnetic fieldgenerated by the loop in order to navigate. The intention is to enablethe robot, placed near to the loop, to determine on which side of theloop it is positioned and to enable it to follow the loop.

What should be known about this type of wiring of conductors as used inthe navigational control station 3 is that conductors in close proximitywith opposing current increase the inductance of the loop. The electricconductors can be made as etched conductors in a carrier or be wound asmulti-conductor cables, preferably mounted on a carrier. The advantageof a carrier is that the user does not need to make an effort installingthe loop. If the carrier consists of mainly a plane disc, this can beinstalled in a suitable way. If the disc also is used in conjunctionwith a battery charger, a robot can, by driving up onto the disc, easiermove itself in towards the charger's pole contacts (the charger is notshown in FIG. 1, but can preferably be read as the signal generator 1).

The opposed, parallel parts of the electric conductors, with opposeddirections of current, may not be placed to close to each other(corresponds to a long and narrow terminal area). That would result inproblems with the magnetic field, in turn significantly reducing therange of the magnetic field. A suitable choice of terminal surface areais 60×60 cm.

The current, which is generating the time-variable magnetic field in thenavigation control station 3, can have different characteristics. Acurrent of an alternating current character, such as a sinusoidalcurrent, is a conceivable possibility. If a sinusoidal current of 0.2 Ais used and resonance circuits are used for the robot's sensing, it ispossible to achieve a navigational control area of the remote systemwith a radius of several metres. That implies that a loop of 10 turnswould result in a value of 2 ampere-turns.

FIG. 2 shows another type of conceivable current signal that thenavigation control station 3 could operate with. That signal is wellsuited for the type of navigation control system as intended in theinvention. The figure does not take the conductors' inductance intoaccount, so a more correct figure should really show how the current isdelayed and rises versus time in accordance with the application. Thepulse-generated magnetic field that propagates out from the controlstation 3 embodies the characteristics corresponding to the current. InFIG. 2, the pulse 7 corresponds to a main pulse A0 with a length of 100μs. The choice of pulse length shall not be seen as a limitation of theinvention but only represents suitable values in this embodimentexample. The period time 8 for this, which is also the period time forthe entire variant of current signals, is preferably 12 ms, whichcorresponds to the frequency of 83 Hz. The pulse N79 has a length of 50μs, has the same period time 8 and occurs 7 ms 10 after A0. Note that 1ms is the shortest possible distance to allow the control unit's 15amplifier to be reset after the pulse A0. The resetting time depends onthe fading out of the A0 signal in the amplifier's connectingcapacitors. The pulse F9 11 has the same length and period time as N7and occurs 9 ms 12 after A0.

Using current pulses of 2 A in a loop of 10 turns results in 20ampere-turns, which under normal conditions means a navigational controlarea for the remote system corresponding to approximately 6 meters'radius. The disadvantage with current pulses is that the possibility touse resonance circuits does not exist. Instead, increased current isneeded for a sufficient control range within the navigational controlarea, within which the sensing unit can detect a magnetic field from thenavigational control unit. Sometimes push-pull is used to achieve anincreased current out of the voltage of 40 V normally allowed in thistype of installation. An increase of the number of ampere-hours isalways desirable, but it also increases the magnetic field. Since thenavigational control system will operate in environments close to humanbeings, it is important to keep the magnetic field low.

Using current pulses facilitates for the robot, which communicates withthe loop 2 and the navigational control station 3 through the magneticfields, to avoid problems of being superimposed with other magneticfields. Since the current pulses occur at different points of time,during short time intervals and by allowing the robot to listen forpulses during the corresponding time intervals only, the system canfilter away other magnetic field noise that could interfere with therobot's function. The control unit can also be allowed to listen for A0pulses 7 and synchronise itself with them. If A0 is not being used, therobot can be synchronised with some other pulse.

The robot is shown in FIG. 3. It comprises a detection device 14, 15, 16as part of the navigational control system. Furthermore, the robot haswheels 13, which is not intended to limit the thought of invention.Caterpillar tracks are an alternative possibility. The detection devicenormally constitute a unit in common, comprising functions for reception14 (henceforth called receiver) of magnetic fields, control 15(henceforth called control unit), processing of the received magneticfield and motor control 16 for controlling the drive motors andadjustable wheels on the robot. The functions are shown as separateunits in the figure, with the intent to clarify that the detection unithas these functions.

In real life, most of the time the separation is carried out by means ofsoftware in a computer unit, where the software is complemented withadditional components for the computer unit. The receiving unit normallycomprises one or several coils, which enclose a ferrite rod placed inthe centre of the respective coil. The coil and the ferrite rod isnormally placed horizontally, but if, for instance, the navigationalcontrol station were vertically oriented, the coil and the rod wouldpossibly have to be rotated to facilitate reception of the magneticfield. If many coils are used, they can be placed in differentdirections. The magnetic field having a field direction mainly parallelto the coil influences the receiving unit by means of the coil detectingthe change in field strength. The control unit receives the signals fromthe receiving unit and processes the information. Subsequently itcommunicates signals to the motor control unit 16, which control themotors (not shown) driving the wheels 10.

A control unit for this type of device has naturally many tasks, forinstance controlling the tools, cutting, cutting device, brushes etcpossibly mounted on the robot. To facilitate this, such a control unitnormally has memory units for storage of software code executed duringoperation. Of main interest for the present invention is its processingof magnetic fields transmitted by a loop and received by the receivingunit 14. Consequently the robot's parts are only schematically shown.The processing is described in further detail below in conjunction withthe presentation of the robot's function.

The task of the navigational control station 3 is to create severalnavigational control areas for the control of the robot in relation tothe navigational control station. By different control areas is meantthat the magnetic fields from the proximity system and the remote systemrespectively do not create equally sized navigational control areas. Themagnetic field transmitted by the navigational control unit can egenerated by a current of suitable characteristics, such as a sinusoidalcurrent or current pulses. The intention of invention is not limited tothe character of the current. The essential thing is that the magneticfields generated around the station are possible to discriminate and tobe interpreted by the sensing unit (14, 15, 16). The vertical magneticfield's direction is described below. Thereby is understood thedirection of the magnetic field in a certain position at a certain pointof time. For pulse systems, the direction is always as shown in thefigures, but for a sinusoidal or similar system the magnetic field ischanging direction all the time.

FIG. 5 shows a possible embodiment of the navigational control station3. The loop 6 is illustratively wound 3 turns in the figure, but it ispossible to use more or fewer turns. The area covered by the loopcorresponds to the area of the station. The station area neednecessarily not have a horizontal extension. The embodiment is suitedfor use with the remote system, which is intended to contribute to thenavigation of the robot when it moves far away from the navigationalcontrol station 3. If the loop were to be illustrated in a verticalposition, the magnetic field would still propagate from the station, butthe field would be rotated 90 degrees.

FIG. 6 shows the magnetic field, as detected by the receiving unit 14,at one point of time. Since the loop of the example preferred embodimentis horizontally positioned, the vertical coil detects the verticalmagnetic field. The coil is positioned 10 cm above the ground. Thestrength and direction of this field constitute the information used bythe robot to navigate. The loop 6 is shown in the upper part of thefigure. The frame 40 illustrates where in relation to the loop thevertical field 41 is changing direction. The reason for the change ofdirection occurring outside the loop is that the parallel parts of theloop with opposite current influence each other to the extent that themagnetic field's change of direction is forced outwards. The phenomenonbecomes stronger the closer to each other the parts of the loop arepositioned.

The graph for the vertical field 41 has its peak value 42 within theloop 6 and its lowest values 43 a somewhere outside the loop. The twopeaks indicate that the field strength decreases with the distance tothe conductor, even within the loop 6. The field strength decreasesrapidly outside the loop. Further down in FIG. 6 it is shown how thevertical field 44 sensed by the robot decreases. The graph is ratherflat, but if the scale of the loop 6 would be decreased, the graph wouldinstead fall rather rapidly within the diagram. The magnetic fielddecreases rapidly with the radial distance to the loop, which applies toall magnetic fields in the navigational control system. Note that thevertical field 44 at the same point of time has a negative direction inrelation to that of the field 41 within the loop.

FIG. 7 presents a view where the conductors' cross-section and themagnetic field's significant direction 45 within the loop 6 is shown.The field direction 45 corresponds to that the signal generator 1 hassent a current moving counter clockwise in FIG. 5-6. The crosses in FIG.7 corresponds to that the current moves inwards in the figure and thedots to that it moves outwards. Note that the vertical magnetic fieldthat is detected by the robot's sensing unit 14, 15, 16 outside thenavigational control area (approximately 6 meters at 20 ampere-hours) ofthe remote system will be so weak, that it can not be detected by thesensing unit.

FIG. 4 shows another possible embodiment of the navigational controlstation 3. The station comprises a right and a left loop 4. Each loop isfor the sake of illustration wound 3 turns, but it is possible to usemore or fewer turns. The area covered by the loops corresponds to thestation area. The station area need not necessarily have a horizontalextension range or extend in the same direction as the loop 6 if theseare combined. The embodiment is suited for use both as the remotesystem, which is intended to direct the robot when it moves far awayfrom the navigational control station 3 and as the proximity system,which is intended to direct the robot when it moves close to thenavigational control station. In FIG. 4 the loops 4 are connected to theconnecting box 17 so that both, at the same point of time, show the samemagnetic field direction 46 within the area enclosed by the respectiveloop 4. The connection can be made by hardware and/or software by thesignal generator 1. This results in a vertical magnetic field patterncorresponding to that shown in FIG. 6. If the loops were to beillustrated in a vertical position, the magnetic field would stillpropagate away from the station, but the field would be rotated 90degrees. The embodiment of the station according FIG. 4 is suitable as aremote system.

In FIG. 8 the loops 4 are connected to the connecting box 17 so thatthey at the same point of time show magnetic fields with directions 50,51 opposed to each other within the area enclosed by the respective loop4. This results in a vertical magnetic field 52, sensed by the receivingunit 14, as shown in FIG. 9. The coil is placed 10 cm above the ground.Even in this case the change of direction 53 is forced outwards. Thepeaks of graph 52 illustrate the fact that the field strength decreaseswith the distance to from the conductors, also within the loops. Theshape of the peak depends on where the coil is positioned in relation tothe loop. Outside the loop the magnetic field 52 decreases faster thanin the case with a loop 6, because the fields from the two loopsinterfere with each other. At 20 ampere-turns (2 A and 10 turns), therange of the navigational control area is approximately 1 meter awayfrom the station. In the lower part of FIG. 9, the sensed magnetic field54 is shown a certain distance from the loop. A line 55 illustrateswhere the co-operation of the two magnetic fields 50, 51 results in azero amplitude field. A change of field direction takes place along thisline, i.e. the sensing unit detects a change of field direction if therobot crosses this line. Further out the line will propagate as a funneldue to a decreasing field. Within the funnel, the sensing unit does notessentially detect any field. The propagation of the funnel varies withtime depending on interference generated within and outside thenavigational control system and on that the fields from the two loopsco-operate with each other.

The essential field direction 56 of the magnetic fields around the 4conductors is shown in FIG. 10. The field direction 56 corresponds tothe generator having sent a current moving counter-clockwise in theright loop and clockwise in the left loop. The crosses corresponds tothat the current moves inwards in the figure and the dots to that itmoves outwards.

The connection box 17 is mentioned in the latest described embodiment ofthe navigational control station with two loops 4. By using currentpulses and letting the signal generator control the connections based onthese pulses, a useful time separation of magnetic fields can beachieved. If there is an outer loop, the synchronisation pulse A0 7 canbe allowed to go through the outer loop 2. Alternatively, A0 can be sentthrough some other existing loop. The pulse N7 9 can for instance gothrough the loops 4 connected according to FIG. 8 and the pulse F9 11 gothrough the loops 4 connected according to FIG. 5. Thereby oneembodiment of loops in the navigational control station 3 may suffice.Control implies a continuous change in the connection of the loops basedon which pulse is approaching. This results in that a combined remoteand proximity system is achieved. The receiving unit 14 will register upto 3 magnetic fields, which are generated at different points of time,see FIG. 2, and controls its movements based on one of them.

Alternatively, a type 6 loop can be used for the remote system and thetwo loops 4 for the proximity system, where the loops propagate in thesame or different directions. Sometimes it is desirable to cause achange of directions for the magnetic fields that coincide in the spacefor the proximity system and the remote system. In such cases a separateremote loop enclosing the proximity loops are preferred. Since thechange of direction of the proximity loops 4 is forced further out thanthat of the remote loop 6, changes of direction coinciding in the spaceare achieved by this arrangement.

When choosing type of current in the system, it is important to considerwhether a reference is needed. The intention with the navigationalcontrol of the robot as described below is that the sensing unit whennecessary has the possibility to decide in relation to what the field'sdirection shall be determined. If the system comprises one remote systemonly, one sinusoidal signal only for generating the magnetic field 42may very well suffice. The robot will, inside the navigational controlarea of the remote system, navigate according to the field strengthonly, whereby the sensing unit, when coming inside the loop, takes intoaccount that the field is changing directions. However, for manoeuvringwithin the navigational control area generated by the proximity system,at least two signals with different frequencies (multiple in relation toeach other) are required to enable the sensing unit to make acomparison. Otherwise the robot will not know what is right and left inthe proximity system.

Due to the two signals generating magnetic fields that change directionsat a certain ratio depending on the signal's frequency relation to eachother, the direction of the respective magnetic fields at a certainpoint of time is compared. The same two signals are transmitted throughboth loops 4. If the navigational control system comprises remote aswell as a proximity system, a signal can be transmitted through theproximity system and the remote system. There is a need for at least twosignals in the navigational control system. If current pulses are used,the comparison problem does not arise because the sensing unit knows themagnetic field direction due to the current pulses being transmitted inone direction only. A third sensing alternative is to transmit fieldswith different directions. Such a method requires coils so positionedthat they can detect the different fields.

The function of the navigational control system shall now be describedwith reference to FIGS. 11-12. The main objective with the communicationbetween the robot and the navigational control station 3 is mainly toenable the robot to control its movements in relation to the stationwithout having to follow the loop. The signal generator 1 generatescurrent in the navigational control station 3 which in turn generatesmagnetic fields, which create the navigational control areas withinwhich the robot can be controlled. The magnetic field is picked up bythe receiving unit 14 on the robot and the control unit 15 filters outremaining magnetic field noise from the picked up magnetic fields.

Irrespective of the type of current, the control unit 15, containing anumber of algorithms to handle the received magnetic field, will use theinformation contained in the magnetic field for different purposes. Whenan algorithm for sensing the magnetic field from the navigationalcontrol station 3 is activated (for instance by the battery charginglevel starting to become low), it makes sure that the robot 5, whenmoving detects that the field strength changes, depending on algorithmchooses to move towards a higher field strength, follow a field line forconstant field strength, move towards lower field strength or stop andpossibly turn. The detection is naturally not based on the variations ofthe current within each signal period but on the magnetic field strengthor the ration between two magnetic fields. The robot is consequentlymanoeuvring itself based on the detection of the field's properties.

In the remote system case, two of the robot's five possible paths ofmovement are shown in FIG. 11. When the algorithm for detection of themagnetic field 43 and 44 is activated, it is, to achieve a movement path46, ensured that the robot, when moving and detecting an increasingfield strength, continues straight forward. If the field strength isinterpreted as unchanged when the robot is moving, it turns 90 degreesin any direction. If the field strength is interpreted as decreasingwhen the robot is moving, the robot turns 180 degrees. The movementopens the possibility to use the remote system only to direct the robot.This would result in that the robot finds its way in towards the middleof the navigational control station 3 from any undefined direction. Inthe case of an alternative movement path 47, the robot seeks an isobar48 corresponding to a specific magnetic strength and then follows it.When the receiving unit 14 comes inside the loop and the field changesdirection, the algorithm takes this into account. When using the remoteloop, the robot is not dependent of knowing the field direction.

In the case with the proximity system, FIG. 12 shows a possible movementpath for a different algorithm. The generated field in the proximitysystem propagates approximately one meter out from the loops 4. When thealgorithm for sensing the magnetic fields 52 and 54 is activated, itmakes sure that the robot, when in movement and intersecting the line55, which corresponds to a change of field direction, with the wheels asa counting reference continues running until the rear axle isessentially positioned above the line. It subsequently turns until thereceiving unit once again senses a change of direction. The robot thenfollows the line in towards the loops. The algorithm knows in whichdirection the robot shall turn by sensing the relationship between themagnetic fields transmitted by the respective loop.

When the robot's sensing unit comes essentially inside the propagationarea of the navigational control station, the magnetic field changesdirections. Where the change of direction takes place has been describedin the text. Simultaneously, the field strength will again start todecrease. In what way the field strength will change depends on whethera proximity system or remote system with one or two loops are used. Whenthe field is changing, the robot is positioned very close to the stationand will find out by means of the field change. This constitutes asmaller problem for the proximity system, since the robot, by followingthe line 55, already has a satisfactory way of manoeuvring. To primarilywatch out for is that the change in field direction between the loops 4is very strong.

On the other hand, the field strength in the remote system will againstart to decrease within the station area. One possibility is that thesensing unit reverts its calculations and instead finds its way towardslower field strength as long as it once again does not detect a changein field direction. Such a change would of course indicate that thesensing unit once again were in the vicinity of the station.

Using the loop 6 only for navigation means that fine-tuning against thecontact poles is not achieved but instead the charging station must bedesigned as a cap with possible contact from all directions. With such acap, the navigational control station can have the embodiment as shownin FIG. 5 or propagate in a circular manner. The robot will in that caseonly steer towards higher field strength and, independent of from whichdirection it comes, find the poles of the cap. By combining theproximity and remote system and use movement path 47 and 57, the robotcan first follow an isobar 48 for the remote system until it intersectsthe line 55, then finding its way in along the line. Alternatively therobot can follow an isobar for the proximity system. The isobar for theproximity system to a certain extent runs parallel to the line 55, so inprinciple this movement would lead the robot all the way in. However,because the robot is big and slow, following the isobar in such a way isoften not enough. The robot instead uses the line 55.

As regards the robot, possible fields of applications for this type ofnavigational control system are operating robots such as grass-cuttingrobots and vacuum cleaning robots. These comprise operating tools suchas knives or brushes. It would for instance be conceivable that thecontrol unit controls their operation based on the informationtransmitted by the loops. For instance, the knives are broken off as aresult of certain movements. Other robots could be cleaning robots forwet-cleaning of large floor areas, for example in industrial buildings.The choice of field of use is not essential, but instead the applicationrelates to the search system.

The intention of the presented embodiments is to concretise theinvention and shall not be interpreted as a limitation of the invention.Embedded in the thought of invention is also the possibility to equipthe system with more or fewer loops and signal generators, for instancein order to set boundaries around surfaces, across which the robot isintended to move, control the robot along a loop and possibly use morethan one robot. Further embodiments are therefore contained within thethought of invention as specified in patent claim 1. The invention isconsequently not limited to what is described above or to the embodimentshown in the drawings, but the arrangement can be used within all areaswhere search systems for autonomous devices on wheels, normallydesignated robots, come into use.

1. Method for maneuvering a self-propelling device (5) by means of anelectronic navigational control system comprising at least anavigational control station (3) connected to at least one signalgenerator (1) and one sensing unit (14,15,16) arranged at theself-propelling device (5), whereby the sensing unit (14,15,16) at leastsenses an, in the air-medium propagating, time and space varyingmagnetic field, transmitted by the navigational control station (3) andin turn retransmits at least one, by the sensing unit (14,15,16)processed signal to at least one drive source that contributes to thedevice's (5) movements across a surface, the signal generator (1) sendsa current through the navigational control system (3), the currentgenerating the time and space varying magnetic field (43,44,52,54),whereby the sensing unit (14,15,16) maneuvers the device (5) based onthe properties of the sensed magnetic field (43,44,52,54), characterisedin that said sensed magnetic field (43,44,52,54), in an area mainlywithin the range of the navigational control station (3), at least atone point of time has different directions (50,51).
 2. Method accordingto patent claim 1 characterised in that the device (5), when movingmainly outside the range of the navigational control station and sensinga change in the magnetic field (44,54), maneuvers itself in relation tothe navigational control station (3) so that it by means of one or manymaneuvers will approach, essentially stay at a constant distance from ordistance itself from the navigational control station (3), alternativelystop and/or turn.
 3. Method according to patent claim 2 characterised inthat the device (5), when moving in a course direction and senses anunchanged magnetic field strength (44,54), changes directions 90degrees, that the device, when moving in a course direction and sensesan increased magnetic field strength (44,54), continues in the samecourse direction and that the device, when moving in a course directionand senses a decreased magnetic field strength (44,54), changes coursedirections 180 degrees.
 4. Method according to patent claim 2characterised in that the device (5) moves in a course direction thatcorresponds to that the sensed magnetic field (44, 54) is constant. 5.Method according to patent claim 2 characterised in that the device (5),when sensing that the magnetic field (44,54) changes directions (55),continues to move a certain distance in the same direction, then stopsand turns until it again detects that the magnetic field (44,54) changesdirections (55), whereupon it moves essentially in the same direction asa line (55), which ties together points where the sensed magnetic field(44,54) changes directions.
 6. Method according to patent claim 1characterised in that the sensing unit (14,15,16), when sensing themagnetic field (43,52) within the range of the navigational controlstation (3), adapts its processing of the sensed magnetic field (43,52).7. Method according to patent claim 1 characterised in that at least onesignal generator (1) sends a first current trough the navigationalcontrol station (3), whereby the magnetic field (43,44), generated bythe current at a point of time mainly inside the range of thenavigational control station (3), has a direction essentially opposed tothe direction of the magnetic field (43,44) at the same point of timemainly outside of the mentioned range.
 8. Method according to patentclaim 1 characterised in that at least one signal generator (1) sends asecond current through the navigational control station (3) and thementioned (1) or another signal generator (1) sends a third currentthrough the navigational control station (3), whereby the magnetic field(43,44), generated by the second current in a second area mainly withinthe range of the navigational control station (3), at a point of timehas a direction essentially corresponding to the direction (46) of themagnetic field (43,44) generated by the third current at the same pointof time in a third area mainly within the range of the navigationalcontrol station (3).
 9. Method according to patent claim 1 characterisedin that at least one signal generator (1) sends a second current troughthe navigational control station (3) and the mentioned (1) or anothersignal generator (1) sends a third current through the navigationalcontrol station (3), whereby the magnetic field (52,54), generated bythe second current in a second area mainly within the range of thenavigational control station (3), at a point of time has a directionessentially opposite to the direction (50,51) of the magnetic field(52,54) generated by the third current at the same point of time in athird area mainly within the range of the navigational control station(3).
 10. Method according to patent claim 8 characterised in that thesecond current corresponds to the third current.
 11. Method according topatent claim 9 characterised in that outside and within the range of thenavigational control station an undefined area (55) is created thatessentially defines two areas, which at a point of time have magneticfields essentially opposed to each other.
 12. Method according to patentclaim 8 characterised in that the direction (46,50,51) of the magneticfields (43,44,52,54) generated in the second and third areas depend onthe properties of the sent currents.
 13. Method according to patentclaim 1 characterised in that at least one current in the systemconstitutes a sinus component.
 14. Method according to patent claim 1characterised in that at least one current sent in the system most ofthe time is in a state of rest when it is mainly constant, wherebyperiodically the state of rest is interrupted by at least onecharacteristic reference current pulse (7,9,11).
 15. Method according topatent claim 14 characterised in that the sensing unit (14,15,16),knowing the properties of the reference pulse (7), adapts the timeintervals within which the sensing unit (14,15,16) sense magneticfields.
 16. Method according to patent claim 15 characterised in thatadaptation means that the sensing unit (14,15,16) synchronises theunit's (14,15,16) working frequency in the time domain based on thereference current pulse (7).
 17. Method according to patent claim 15characterised in that adaptation means that the sensing unit (14,15,16)synchronises the properties of the time intervals in the time domainbased on the properties of the reference current pulse (7,9,11). 18.Method according to patent claim 14 characterised in that each signalgenerator (1) in the navigational control system synchronises its sentcurrent pulses (7,9,11) with the other current pulses (7,9,11) in thesystem so that no current pulses (7,9,11) coincide at the same timeduring the same signal period (8).
 19. Method according to patent claim8 characterised in that the magnetic field's (43,44,52,54) direction(46,50,51) within the second and the third areas respectively at a pointof time depends on the properties and the occurrence of current pulses(7,9,11).
 20. Method according to patent claim 8 characterised in thatwhen a first current pulse N7 (9) occurs, the magnetic field (54) in thesecond area, at a point of time, shows a direction (50) essentiallyopposed to the direction (51) of the magnetic field at the same point oftime in the third area and when another current pulse F9 (11) occurs,the magnetic field (54) in the second area, at a point of time, shows adirection (46) essentially corresponding to the direction (46) of themagnetic field in the third area.
 21. Electronic navigational controlsystem for a self-propelling device (5), the system comprising at leastone navigational control station (3) connected to at least one signalgenerator (1) and a sensing unit (14,15,16) arranged at theself-propelling device (5), whereby the sensing unit (14,15,16) sensesat least one time and space varying and in the air medium propagatingmagnetic field, at least transmitted via the navigational controlstation (3), in turn re-transmitting at least one, by the sensing unit(14,15,16) processed, signal to at least one driving source thatcontributes to the device's movements across an area, the systemcomprises means by which the signal generator (1) sends a currentthrough the navigational control station (3), the current generating thetime and space varying magnetic field (43,44,52,54), whereby the sensingunit (14,15,16) comprises means by which the device (5) is maneuveredbased on the properties of the sensed magnetic field (43,44,52,54),characterised in that that said sensed magnetic field (43,44,52,54), inan area mainly within the range of the navigational control station (3),at least at one point of time has different directions (50,51). 22.Electronic navigational control system according to patent claim 21characterised in that at least one current being sent in the systemduring the main part of the time is in a state of rest, where it isessentially constant, whereby the state of rest is periodicallyinterrupted by at least one characteristic reference current pulse(7,9,11).
 23. Electronic navigational control system according to patentclaim 21 characterised in that the navigational control station (3)comprises a first loop (6) which surrounds a first area, said loopextends in one plane.
 24. Electronic navigational control systemaccording to patent claim 23 characterised in that the navigationalcontrol station (3) comprises a second and a third loop (4), whereby thesecond loop (4) surrounds a second area and the third loop (4) surroundsa third area.
 25. Electronic navigational control system according topatent claim 24 characterised in that the respective loop (4,6) extendsin one plane.
 26. Electronic navigational control system according topatent claim 23 characterised in that the plane extends parallel to theground surface or vertical to the ground surface.
 27. Electronicnavigational control system according to patent claim 23 characterisedin that at least one loop constitutes an electric conductor that isplaced above, in or below the continuous surface across which the deviceis intended to move.
 28. Electronic navigational control systemaccording to patent claim 23 characterised in that at least one loopconstitutes a continuous electric conductor that is wound in more thanone turn.
 29. Electronic navigational control system according to patentclaim 28 characterised in that the electric conductor constitutes a fixguide path placed on a carrier.
 30. Electronic navigational controlsystem according to patent claim 21 characterised in that by aself-propelling device (5) is meant an operating robot comprising aoperating system for working on the surface across which the robot ismoving.
 31. Electronic navigational control system according to patentclaim 30 characterised in that the operating system is controlled basedon information received and/or stored for processing by the sensing unit(14,15,16).
 32. Electronic navigational control system according topatent claim 30 characterised in that the robot constitutes alawn-mowing robot, whereby the operating system constitutes kniveswhich, when moving, cut off the biological material growing on thesurface.
 33. Electronic navigational control system according to patentclaim 30 characterised in that the robot constitutes a vacuum cleaningrobot, whereby the operating system comprises the parts with which avacuum cleaning robot is normally equipped for cleaning the surface fromdirt, for instance a rotating brush and a suction device.
 34. Electronicnavigational control system according to patent claim 30 characterisedin that the robot constitutes a cleaning robot, whereby the operatingsystem comprises the parts with which a cleaning robot is normallyequipped for cleaning the surface from dirt, for instance tools forwet-cleaning.
 35. Method according to patent claim 9, wherein the secondcurrent corresponds to the third current.
 36. Method according to patentclaim 9, wherein the direction of the magnetic fields generated in thesecond and third areas depend on the properties of the sent currents.